1. Field of the Invention
The invention relates generally to a method of manufacturing a capacitor in a semiconductor device. More particularly, the invention relates to a method of manufacturing a capacitor in a semiconductor device using a metal material as a lower electrode.
2. Description of the Prior Art
Generally, as a semiconductor device is highly integrated, it is necessary that both the size of the device and the thickness (Tox) of an effective oxide film be reduced. Therefore, in order to manufacture a more reliable device, it is necessary that an electrical characteristic such as a leakage current be improved while change in the capacitance depending on a bias voltage is reduced. In order to improve this characteristic, a capacitor of a MIM (metal-insulator-metal) structure has been developed, in which a metal material is used as an upper electrode and a lower electrode is used instead of conventional polysilicon. When a metal electrode capacitor is formed, in order to manufacture reliable devices capable of preventing oxidization of a lower electrode material due to a thermal process after deposition of the entire film, and to improve characteristics such as the thickness of an effective oxide film and a leakage current in a capacitor, a method of depositing a good quality capacitor dielectric film and controlling thermal process conditions become very important factors.
When a capacitor including Ta2O5 in a memory device is manufactured, if noble metal materials such Ru, etc. are used as a lower electrode, as the energy barrier with polysilicon, that is, the work function is great, it is possible to reduce the thickness of an effective oxide film and to reduce a leakage current in the thickness of the same oxide film.
When a Ta2O5 dielectric film is deposited, however, a subsequent annealing process is required in order to secure a dielectric characteristic of a capacitor since oxygen content is low and the film includes impurities such as carbon and hydrogen. In an annealing process under oxygen atmosphere at high temperature in order to secure a dielectric characteristic of the Ta205, if the temperature of the annealing process is too high or the time of the annealing process is too long, the lower electrode is oxidized to create an unnecessary oxide at the interface the Ta2O5 film and the lower electrode.
In a structure in which TiN is used as a barrier film, Ru is used as a lower electrode and Ta2O5 is used a dielectric film, if an annealing process for securing a dielectric characteristic of a Ta2O5 film is performed, a RuO2 film is formed at the interface of the Ru lower electrode and the Ta2O5 film. At this time, as the RuO2 film is additionally formed, depending on the surrounding oxidizing condition, and not by a given oxidization condition applied to it, the quality of the film is degraded and the thickness of it becomes nonuniform. The RuO2 film is grown while the surface of the Ru lower electrode is oxidized during the annealing process. Thus, not only a lifting phenomenon of the Ta2O5 film is generated by expanded volume due to growth of the RuO2 film, but also oxygen contained in the Ta2O5 film is diffused into the Ru lower electrode. Due to this, there is a problem that a dielectric characteristic of the Ta2O5 film cannot be sufficiently obtained. Also, as the thickness of the RuO2 film is nonuniform, the surface roughness at the interface of the Ru lower electrode and the Ta2O5 film is increased to lower the dielectric characteristic of the Ta2O5 film.
In addition, if oxygen is diffused into the TiN barrier film via the Ru lower electrode, the oxygen reacts with TiN to form a TiN barrier film made of TiO or TiON, which results in lowering of the quality of the TiN barrier film to degrade an electric characteristic of the device.
A method of manufacturing a capacitor in a semiconductor device according to the invention includes the sequential steps of forming a polysilicon film, a barrier film, and a Ru film on an oxide film formed on the semiconductor substrate, and then patterning the polysilicon, barrier, and Ru films to form a lower electrode; forming a RuO2 film on the Ru film; forming a dielectric film on the RuO2 film and then performing an annealing process; and forming an upper electrode on the dielectric film.